This application addresses the program announcement R21 PA-13-303. Our focus is on understanding how epigenetic mechanisms controlling developmental patterns contribute to the onset and progression of osteoarthritis. While osteoarthritis (OA) is the most prevalent form of arthritis, affecting tens of millions of Americans, relatively little is known about the mechanism(s) implicated in the early stages of the disease. As a consequence of our poor understanding of OA, there is no proven disease-modifying therapy available. OA is characterized by the destruction of the cartilage matrix, which is essential for maintaining the integrity of the joint surfaces. In OA disease, chondrocytes, the unique cell type of articular cartilage, undergo hypertrophic- like changes that resemble patterns observed during development. To some extent, those changes comprise alterations of the DNA methylation status that lead to abnormal gene expression and cell function. We hypothesize that the abnormal gene expression observed in OA chondrocytes in vivo relates to alterations in DNA methylation that recapitulate developmental events, inappropriately leading articular chondrocytes to a hypertrophic-like state. In this project, we will utilize Enhanced Reduced Representation of Bisulfite Conversion to profile the DNA methylation status of growth plate chondrocytes, and to define DNA methylation patterns associated with chondrocyte hypertrophic differentiation and linked to changes in gene expression, assessed by RNA sequencing. We will then establish parallels with alterations in DNA methylation and gene expression that occur at progressive stages of OA disease, using human OA cartilage samples and a mouse model of surgically-induced OA. These approaches will allow us to define epigenomic alterations that lead to OA disease initiation and progression. Ultimately, the successful completion of our experiments should lead to the development of novel therapeutic strategies for early OA by targeting disease-related alterations in epigenomic regulation.